docs: update required zig version in README.md

closes #292

README.md

@@ -45,7 +45,7 @@ Or check your favorite local system package repository.
 
 Make sure your system meets the requirements listed above.
 
-Flow builds with zig 0.14.1 at this time. Build with:
+Flow builds with zig 0.15.1 at this time. Build with:
 
 ```shell
 zig build -Doptimize=ReleaseSafe

src/renderer/vaxis/renderer.zig

@@ -112,7 +112,7 @@ var panic_cleanup: ?struct {
 } = null;
 
 pub fn panic(msg: []const u8, error_return_trace: ?*std.builtin.StackTrace, ret_addr: ?usize) noreturn {
-    _ = error_return_trace; // TODO: what to do with this in zig-0.14?
+    _ = error_return_trace;
     in_panic.store(true, .release);
     const cleanup = panic_cleanup;
     panic_cleanup = null;